Northwest of Mutant Bash TV, up a hill, is located Crazy Joe's place by a swamp (with Night Blossoms in it). A hermit by the name of Crazy Joe living here sports a Doom 3 shirt, as one of the many homages to id's other acclaimed franchises.
After clearing the Gearhead Vault you can re-enter it as many times as you want without dealing with enemies. Sprint up to the third floor where there is the big tree in the courtyard and the ATM machines just through the doors in the other room. If you interact with the ATM machines you get cash, then simply sprint and leave the vault and re-enter. You can repeat this for infinite cash. If you linger and casually interact with the ATMs, the payouts are $6, $8, $12-- but if you move quickly and interact with the machines as fast as you can, the payouts are $50, $70, $80 per ATM, particularly from the ATMs to the left as you enter the room (it might just be the last 3 ATMs that you interact with).
In Subway Town you can buy rotating "deals" from Stew. Sometimes you can purchase items at a discount that can immediately be sold at Jani's Supplies at a higher price. For example, Stew will sell you Viper Rockets for $66 which you can sell to Jani for $75. Repeat as often as you like to continue to make a profit.
For easy money by winning card games, go to Subway Town and challenge the woman to a 'Normal' game with the following cards:
RC Car Bomb
This should fill or almost fill your points for allocating cards. I used this deck and won $5000 in less than an hour. It works because you are guarenteed to get all your attacking cards out. However, it is not 100% undefeatable, but I won 95% of the time. It may take some getting used to, but a definite pattern should emerge.
The Quake room, located in the Wasted Garage, can be accessed only after you press three well-hidden red buttons in the area. If you recall, the Wasted Garage is where you were asked to retrieve a distributor cap item during an earlier mission. It is recommended that you complete said mission and re-enter the Wasted Garage from the back entrance.The three buttons are difficult to find: one is located under a night stand, the other between a fallen file cabinet and the window, and the last behind a red tool cabinet. Each makes a Quake-like sound and glows for an instant when pressed. After all three buttons are activated, a hallway marked by a red Quake symbol leads to some stairs and to a portal that takes you to the hidden Quake room. Inside, you'll find the Shambler Plush in the center. To leave, you must step on the tile in the area from which you came.
With your pistol equipped, aim at an item with the scope (monocular). As you let go of the left trigger (zoom button), tap the PICK UP button fast and repeatedly. If done correctly, you should pick up the item and have it in your inventory, this also works on dead guards. The key is that, for some reason, the icon to pick up an item pops up when you zoom out but only for a fraction of a second. Note: A future update might patch this!
In the Ghost Hideout, there's a sequence in the very first mission, Quell the Bandit Threat, where you get stabbed in a cutscene and taught how to use the Defibrillator. After this, you exit the 'killing room' into a hotel room-like area, clear out all the bandits and head to the back of the room toward a painting on the wall. Between the TV and the painting in this room, you can open up a section of wall. Behind it is a pixel Wolfenstein room with the Wolf Goblet inside. You can sell it for 150 dollars.
After completing the initial game missions and entering wellsprings for the first time, you are given the chance to play some mini-games with the locals. You have to meet with the mayor first and get your own garage and your replacement armor for your ark suit. After gettingyour armor its time to play. If you don't have any start up money and nothing to sell, look on the mayors desk in his office on the bottom right corner. You will see a vault boy bobblehead worth a whopping $150! Sell the bobble head and look for an alley where some locals are squatting near a game board with some holograms on it. The game is simple; you get three chances to roll the dice. After each roll the dice will either come up a skull or a crosshair. If you get a crosshair, the sheriff hologram in the middle shoots and destroys a mutant hologram. If you take out every mutant before the end of the third role than you win, if not, you lose the money you bet. You can bet up to $25 per game. If you get four crosshairs in the first round, you get 10x the money you bet back in winnings. If you defeat all the mutants by the second round than you get 4x your winnings, and if you defeat all of them by the end of the third round then you break even. It seems to be random, so just keep playing until you win.
Now here is the hint;save your game before you play. If you win enough money to make more than you started out with, exit the minigame and save, then go and play again. If you lose more money than you win, simply load up your save and try again. I started with $150, in less than an hour I had over $725! This helps make infinite money to stock up on ammo and items early in the game if you are willing to take the time to do it.